List of Past CTC Theory Lunches : 01-Jan-2010 to 01-Jun-2010

Date:   Monday 25-Jan-2010
Speaker:   People who attended the AAS Meeting (Jan 3-7)
Title:   Highlights of the AAS Meeting (Jan 3-7)

Date:   Monday 01-Feb-2010
Speaker:   Sean O'Neill (UMD)
Title:   The Search for Quasi-Periodic Oscillations in Simulations of Black Hole Accretion Disks

Date:   Monday 08-Feb-2010
Speaker:   Demosthenes Kazanas (NASA/GSFC); RESCHEDULED (due to snow)
Title:  1. "The Chiral Magnetic Fields of AGN Jets", or 2. "Echoes of the Kerr Metric : QPOs from totally random Light Curves"

1. We have proposed that the magnetic fields of AGN accretion disks can be built by the continuous action of the Poynting Robertson battery and the accretion process. In this mechanism the poloidal field direction is always parallel to Omega. One can then show that the toroidal field direction is always in the same sense (the fields are chiral). Observations seem to provide support for this notion.

2. Random X-ray flares in accretion disks, if taking place within the BH ergosphere lead to echoes of the original flare with a constant lag ~ 14 M. These lags manifests their presence in the power spectra as harmonically spaced QPOs of frequency 1/14M ~ 1.4 kHz (10M_{\odot}/M).

Date:   Monday 15-Feb-2010
Speaker:   Cole, Derek, and Soko
Title:  Recent Papers

Cole talked about "Increasing the Scientific Return of Stellar Orbits at the Galactic Center" by Yelda, Ghez, & Lu et al. (

Derek talked about "Earth encounters as the origin of fresh surfaces on near-Earth asteroids" by Binzel, Morbidelli, & Merousane et al., 2010, Nature (

Soko talked about two papers on thermal emission from an exoplanet called WASP-19 b: "H-band thermal emission from the 0.79-day period planet WASP-19b" by Anderson, Gillon, & Maxted et al. (, and "Ground-based detection of thermal emission from the exoplanet WASP-19b" by Gibson, Aigrain, & Pollacco et al. (

Date:   Monday 22-Feb-2010
Speaker:   Guilhem Lavaux (UIUC)
Title:  The velocity field of the 2MASS Redshift Survey and its cosmological implications

A valuable source of information on the distribution of dark matter lies in the peculiar velocity field of the galaxies. Unfortunately, these velocities are very difficult to observe. I present here an alternative approach to estimate these velocities which relies on reconstructing them directly from redshift catalogs. In particular, I use the so-called Monge-Ampere-Kantorovitch reconstruction method.

Having tested this method on mock galaxy catalogs, I apply this method to a real galaxy sample: the 2MASS Redshift survey. I study the origin of the motion of the Local Group relative to the Cosmic Microwave Background dipole. In particular, I concentrate on the problems that lie beyond 40 Mpc/h and the constraints put by the large scale bulk flows on the cosmological parameters. Having studied the bulk flow, I make a direct comparison of the reconstructed velocities and the observed distances in our neighborhood of 30 Mpc/h. This comparison yields an independent estimate of the density parameter, which can be used to reduce the degeneracies in the parameter space of the present cosmological cold dark matter model.

Finally, I use the reconstructed peculiar velocities to produce the most precise simulation of the Local Universe. I discuss some of the applications of this simulation.

Date:   Monday 1-Mar-2010
Speaker:   Chris, Cole, and Bruno
Title:  Recent Papers

Chris talked about "The Spin of the Black Hole in the Soft X-ray Transient A0620--00" by Gou, McClintock, & Steiner et al., submitted to ApJL (

Cole talked about "A mass estimate of an intermediate-mass black hole in omega Centauri" by Miocchi, A&A (

Bruno talked about "Exploring binary-neutron-star-merger scenario of short-gamma-ray bursts by gravitational-wave observation" by Kiuchi, Sekiguchi, Shibata, & Taniguchi, PRL (

Date:   Monday 8-Mar-2010
Speaker:   Hao Gong (UMD)
Title:   Dense core formation in supersonic converging flows

Date:   Monday 15-Mar-2010
Speaker:   Spring Break

Date:   Monday 22-Mar-2010
Speaker:   Demosthenes Kazanas (NASA/GSFC)
Title:  The Chiral Magnetic Fields of AGN Jets

We have proposed that the magnetic fields of AGN accretion disks can be built by the continuous action of the Poynting Robertson battery and the accretion process. In this mechanism the poloidal field direction is always parallel to Omega. One can then show that the toroidal field direction is always in the same sense (the fields are chiral). Observations seem to provide support for this notion.

Date:   Tuesday 30-Mar-2010
Speaker:   Eli Dwek (NASA/GSFC)
Title:  The Big Crash: Infrared and X-ray Observations of the Interaction of SNR 1987A with the Equatorial Ring, and their Interpretation


Date:   Monday 05-Apr-2010
Speaker:   Soma De (University of Oklahoma)
Title:  Time dependent radiative transfer in SNe atmosphere and cosmic recombination epoch: Effect on spectra and transition probabilities in a true multilevel framework

The radiative transfer equation (RTE) is effectively the Boltzman equation for photons. This requires one to account for all possible transition rates connecting all energy levels in a given system of species (involving atoms, ions, or molecules). These rates depend on the local radiation intensity and vice versa. This makes the nature of the equations involved in such a scenario highly coupled and the size of the problem very large, especially in a multi-level, multi-species system. I will describe the scope of our general purpose stellar atmosphere code PHOENIX to handle such problems focusing on the cases of SNe and cosmic recombination. I will emphasize my results on core-collapse supernova 1999em and SN1987A atmospheres describing how time dependence in the rate equation arising from long recombination time of hydrogen could affect the Balmer line profile in a supernova's lifetime. I will also describe the effect of escape, photo-ionization probabilities and forbidden transitions in a true multi-level calculation where no assumptions of equilibrium between the higher bound states were made. PHOENIX can also be applied during cosmic recombination epoch. I will present preliminary results on the electron fraction during the the recombination epoch which is obtained by following a time dependent RTE through cosmic recombination. These calculations should shed light on the understanding of CMB power and polarization spectra.

Date:   Monday 12-Apr-2010
Speaker:   Mia Bovill (UMD)
Title:   Are There Too Many Luminous Outer Satellites?

Date:   Tuesday 13-Apr-2010
Speaker:   Stratos Boutloukos (UMD)
Title:  Super-Eddington fluxes from thermonuclear X-ray bursts

Please note that this is a special seminar which takes place on ***Tuesday***.

Date:   Monday 19-Apr-2010
Speaker:   Ed Shaya & Rob Olling (UMD)
Title:   On How to Catch a Binary Star

Date:   Monday 26-Apr-2010
Speaker:   Keigo Fukumura (NASA/GSFC)
Title:  Toward Understanding UV/X-ray Absorbers in the Context of MHD Accretion-Disk Winds in AGNs

I will describe a 2D self-similar MHD accretion-disk wind as UV/X-ray absorbing outflows, often found in radio-quiet AGNs and galactic black hole binaries. In this model a fraction of accreting plasma is assumed to be launched from a thin disk surface and magnetocentrifugally accelerated along magnetic field lines. Photoionized winds progressively absorb an incident radiation as it transmits through the line-of-sight (LoS) plasma of some column density. By coupling to the kinematic properties of the obtained MHD wind solutions we proceed with XSTAR photoionization code to handle radiative transfer along the LoS medium and compute the 2D ionization structure of the wind. Our model, for a given density profile such as n(r) ~ 1/r where r is the LoS distance, is successful in reproducing the observed ionic column density distribution, the so called "absorption measure distribution (AMD)", which is found to be constant (independent) over a large span of ionization parameter (~4-5 orders of magnitudes) at the observed integrated column density, for instance, for IRAS 13349+2438 (Chandra data). Our model further expects (blueshifted) LoS velocities for some characteristic ions; e.g. ~100-300 km/s at log(xi)~2-3 for Fe XVII while ~1,000-4,000 km/s at log(xi)~4-5 for Fe XXV. I will briefly show that the proposed MHD wind is a viable scenario also for the observed high-velocity UV/X-ray absorbers seen in bright quasars. Using our model characterized by only two parameters (mass-accretion rate and LoS angle) I will demonstrate that a combination of AMD and absorption line profile observations can uniquely determine these model parameters and their bearing on AGN population demographics.

Date:   Monday 03-May-2010
Speaker:   Soko Matsumura (UMD)
Title:   Highlights from "The Theory and Observation of Exoplanets"

Date:   Monday 10-May-2010
Speaker:   Ted von Hippel (Siena College)
Title:  White Dwarf Debris Disks and the Fate of Planetary Systems

After a brief introduction to white dwarfs and debris disks, I will present observations from the Spitzer Space Telescope and ground-based telescopes of metal-polluted white dwarfs with circumstellar debris disks. We measure the constituents of the debris disks, the elemental abundances of the material being accreted, and the accretion timescale. Our measurements support the idea that disruptions of asteroids or other planetary minor bodies created these debris disks. Based on the properties of these stars, I interpret the majority of metal-polluted white dwarfs as resulting from planetary system bodies being ground down during the late stages of stellar evolution.

There has been very little theoretical work done on these systems, either on the accretion process from the disks to the stellar surfaces, on the state of the disks, or on the creation of the disks. I will be keen to hear any ideas on how these systems were created and function.

Date:   Monday 07-Jun-2010
Speaker:   Mike Koss (UMD)

Date:   Monday 14-Jun-2010
Speaker:   Enrico Barausse (UMD)
Title:  Gravitational instabilities of superspinars

Superspinars are ultracompact objects whose mass M and angular momentum J violate the Kerr bound (cJ/GM^2>1). Recent studies analyzed the observable consequences of gravitational lensing and accretion around superspinars in astrophysical scenarios. In this paper we investigate the dynamical stability of superspinars to gravitational perturbations, considering either purely reflecting or perfectly absorbing boundary conditions at the "surface" of the superspinar. We find that these objects are unstable independently of the boundary conditions, and that the instability is strongest for relatively small values of the spin. Also, we give a physical interpretation of the various instabilities that we find. Our results (together with the well-known fact that accretion tends to spin superspinars down) imply that superspinars are very unlikely astrophysical alternatives to black holes.

Date:   Monday 21-Jun-2010
Speaker:   Ed Shaya & Soko Matsumura (UMD)
Title:  Kepler Papers

Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller:

Five Kepler target stars that show multiple transiting exoplanet candidates:

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